U.S. patent application number 10/409515 was filed with the patent office on 2004-10-14 for flexible piezoelectric for downhole sensing, actuation and health monitoring.
Invention is credited to Fripp, Michael L., Rodgers, John P., Schultz, Roger L..
Application Number | 20040200613 10/409515 |
Document ID | / |
Family ID | 32869196 |
Filed Date | 2004-10-14 |
United States Patent
Application |
20040200613 |
Kind Code |
A1 |
Fripp, Michael L. ; et
al. |
October 14, 2004 |
Flexible piezoelectric for downhole sensing, actuation and health
monitoring
Abstract
Thin flexible piezoelectric transducers are bonded to or
imbedded into oilfield tubular members or structural members. The
transducers may be used to telemeter data as acoustic waves through
the members. By proper spacing of transducers and phasing of
driving signals, the transmitted signals can be directionally
enhanced or encoded to improve transmission efficiency. The
transducers may be used for health monitoring of the tubular or
structural members to detect cracks, delaminations, or other
defects. The flexible transducers are very thin so that overall
dimensions of tubular or structural members are essentially
unchanged by incorporation of the transducers.
Inventors: |
Fripp, Michael L.;
(Carrollton, TX) ; Schultz, Roger L.; (Aubrey,
TX) ; Rodgers, John P.; (Trophy Club, TX) |
Correspondence
Address: |
CONLEY ROSE, P.C.
5700 GRANITE PARKWAY, SUITE 330
PLANO
TX
75024
US
|
Family ID: |
32869196 |
Appl. No.: |
10/409515 |
Filed: |
April 8, 2003 |
Current U.S.
Class: |
166/250.01 ;
166/177.6; 166/65.1 |
Current CPC
Class: |
E21B 47/16 20130101;
E21B 47/007 20200501 |
Class at
Publication: |
166/250.01 ;
166/065.1; 166/177.6 |
International
Class: |
E21B 043/00 |
Claims
What we claim is:
1. Apparatus comprising: a section of a wellbore tubular member,
and a flexible piezoelectric device bonded to the wellbore tubular
member.
2. Apparatus according to claim 1, further comprising a plurality
of flexible piezoelectric devices bonded to the wellbore tubular
member.
3. Apparatus according to claim 2, wherein the flexible
piezoelectric devices are bonded to the wellbore tubular member at
locations axially displaced along the drill pipe.
4. Apparatus according to claim 3, wherein the locations are
uniformly displaced along the wellbore tubular member.
5. Apparatus according to claim 3, wherein the locations are
nonuniformly displaced along the wellbore tubular member with a
spacing which defines a telemetry code.
6. Apparatus according to claim 2, wherein a plurality of the
flexible piezoelectric devices are bonded to the wellbore tubular
member at the same location with at least one device stacked on top
of another device.
7. Apparatus according to claim 1, wherein each flexible
piezoelectric device has a length, a width and a thickness, has a
mechanical response aligned with the length, and is bonded to the
wellbore tubular member with its length dimension in alignment with
the wellbore tubular member central axis.
8. Apparatus according to claim 7, wherein the thickness dimension
is between 0.001 and 0.025 inch.
9. Apparatus according to claim 8, wherein the thickness dimension
is about 0.010 inch.
10. Apparatus according to claim 1, wherein the flexible
piezoelectric device is bonded to an outer surface of the wellbore
tubular member.
11. Apparatus according to claim 1, wherein the flexible
piezoelectric device is bonded to an inner surface of the wellbore
tubular member.
12. Apparatus according to claim 1, wherein the flexible
piezoelectric device is imbedded within a wall of the wellbore
tubular member.
13. Apparatus according to claim 1, wherein the flexible
piezoelectric device has a length, a width and a thickness, has a
mechanical response aligned with the length, and is bonded to the
wellbore tubular member with its length dimension tilted by thirty
to sixty degrees relative to the wellbore tubular member central
axis, whereby the device may produce torsional waves in said
wellbore tubular member.
14. Apparatus according to claim 1, wherein the flexible
piezoelectric device has a length, a width and a thickness, has a
mechanical response aligned with the length, and is bonded to the
wellbore tubular member with its length dimension tilted by about
ninety degrees relative to the wellbore tubular member central
axis, whereby said device may produce hoop waves in said wellbore
tubular member.
15. Apparatus according to claim 1, wherein the flexible
piezoelectric device comprises a generally flat slab of
piezoelectric material having a length, a width and a thickness,
the slab having grooves along at least one side, said grooves
aligned substantially with the length of the slab and reducing the
slab thickness sufficiently to increase flexibility of the
slab.
16. Apparatus according to claim 15, wherein the grooves have
widths and depths which vary along the length of the slab, whereby
the device generates a shaped waveform.
17. Apparatus according to claim 15, wherein the slab width varies
along its length, whereby the device generates a shaped
waveform.
18. Apparatus according to claim 15, further comprising: first and
second flexible insulating films, and interdigitated electrode
patterns carried on the first and second films, the first and
second films bonded to opposite sides of the slab, with the
electrode patterns in contact with the slab and in alignment with
each other.
19. A borehole telemetry system, comprising: a tubular member
adapted for use in a borehole, and at least one flexible
piezoelectric transducer bonded to the tubular member.
20. A borehole telemetry system according to claim 19, further
comprising a telemetry driver having an electrical output coupled
to the at least one flexible piezoelectric transducer.
21. A borehole telemetry system according to claim 19, further
comprising a plurality of flexible piezoelectric transducers bonded
to the tubular member.
22. A borehole telemetry system according to claim 21, further
comprising a telemetry driver having separate electrical outputs
coupled to each of the plurality of flexible piezoelectric
transducers.
23. A borehole telemetry system according to claim 22, wherein: the
plurality of flexible piezoelectric transducers are axially
displaced along the tubular member, and the telemetry driver
electrical outputs to each of the plurality of flexible
piezoelectric transducers are phase shifted relative to each
other.
24. A borehole telemetry system according to claim 23, wherein the
phase shifts are selected to cause said transducers to generate
directionally enhanced acoustic signals in the tubular member.
25. A borehole telemetry system according to claim 21, wherein the
plurality of flexible piezoelectric devices are nonuniformly
displaced along the length of the tubular member with a spacing
which defines a telemetry code.
26. A borehole telemetry system according to claim 19, further
comprising a telemetry receiver having an electrical input coupled
to the at least one flexible piezoelectric transducer.
27. A borehole telemetry system according to claim 21, further
comprising a telemetry receiver having separate electrical outputs
coupled to each of the plurality of flexible piezoelectric
transducers.
28. A borehole telemetry system according to claim 27, wherein: the
plurality of flexible piezoelectric transducers are axially
displaced along the tubular member, and the telemetry receiver
electrical inputs from each of the plurality of flexible
piezoelectric transducers are phase shifted relative to each
other.
29. A borehole telemetry system according to claim 28, wherein the
phase shifts are selected to cause said transducers to receive
acoustic signals traveling in one direction in the tubular
member.
30. A system for monitoring health of a structural member,
comprising: a structural member adapted for use in an oil
production system, and a first flexible piezoelectric transducer
bonded to the structural member.
31. A system according to claim 30, further comprising a
capacitance detector coupled to the first transducer and measuring
capacitance of the first transducer.
32. A system according to claim 30, further comprising a second
piezoelectric transducer bonded to the structural member at a
location displaced from the first piezoelectric transducer.
33. A system according to claim 32, further comprising: a signal
driver coupled to the first transducer generating an acoustic
signal in said structure, and a signal receiver coupled to the
second transducer detecting the acoustic signal from said first
transducer.
34. A system according to claim 32, further comprising a memory
coupled to said signal receiver storing characteristics of the
signal received by said second transducer.
35. A system according to claim 30, wherein: the structural member
comprises a composite material, and the first transducer is
imbedded in said composite material.
36. A system according to claim 35, further comprising an antenna
coupled to the first transducer and imbedded in the composite
material.
37. A system according to claim 36, further comprising a
transponder having an electromagnetic port for coupling signals to
and from said antenna.
38. A system according to claim 30, further comprising a receiver
coupled to said transducer receiving acoustic signals produced by
defects in the structure.
39. A system according to claim 38, further comprising a signal
analyzer coupled to said receiver identifying the acoustic signals
as indications of defects in the structure.
40. A system for detecting the flow of material through a tubular
element, comprising: a tubular element adapted for flowing
materials in a hydrocarbon production system, and a flexible
piezoelectric transducer bonded to the tubular element.
41. A system according to claim 40, further comprising a signal
receiver coupled to the electrical connection of the flexible
piezoelectric transducer receiving signals produced by materials
flowing in the tubular element.
42. A system according to claim 41, further comprising a signal
analyzer coupled to said receiver identifying the signals as
indications of material flow in the tubular element.
43. A system according to claim 42, wherein said material flowing
in said tubular element comprises liquid material and particulate
material carried in said fluid.
44. A system according to claim 43, wherein the signal analyzer
identifies signals produced by the particulate material.
45. A method for converting between electrical energy and acoustic
energy in a borehole tubular member, comprising bonding a flexible
piezoelectric device to a borehole tubular member.
46. A method according to claim 45, wherein the flexible
piezoelectric device is bonded to a curved surface of the borehole
tubular member.
47. A method according to claim 45, further comprising coupling an
electrical transmitter to an electrical connection of the flexible
piezoelectric device.
48. A method according to claim 45, further comprising coupling an
electrical receiver to an electrical connection of the flexible
piezoelectric device.
49. A method according to claim 48, further comprising using energy
received from the flexible piezoelectric device as an electrical
power source.
50. A method according to claim 48, further comprising charging a
battery with energy received from the flexible piezoelectric
device.
51. A method for telemetering data in a borehole, comprising:
bonding a mechanical connection of a first flexible piezoelectric
device to a tubular member adapted for use in a borehole, and
coupling electrical signals to an electrical connection of the
first flexible piezoelectric device.
52. A method according to claim 51, further comprising: bonding a
plurality of the first flexible piezoelectric devices to the
tubular member at locations axially displaced along the tubular
member, and coupling electrical signals to electrical connections
of each of the plurality of the first flexible piezoelectric
devices.
53. A method according to claim 52, further comprising phase
shifting the electrical signals coupled to each of the plurality of
the first flexible piezoelectric devices, whereby a directionally
enhanced acoustic signal is induced in the tubular member.
54. A method according to claim 51, further comprising: bonding a
mechanical connection of a second flexible piezoelectric device to
the tubular member, and receiving electrical signals from an
electrical connection of the second flexible piezoelectric
device.
55. A method according to claim 54, further comprising: bonding a
plurality of the second flexible piezoelectric devices to the
tubular member at locations axially displaced along the tubular
member, and receiving electrical signals from electrical
connections of each of the plurality of the first flexible
piezoelectric devices.
56. A method according to claim 55, further comprising phase
shifting and combining the electrical signals received each of the
plurality of the second flexible piezoelectric devices, whereby a
directionally enhanced acoustic signal is received from the tubular
member.
57. A method for monitoring mechanical health of a structural
member in an oil production system, comprising bonding a mechanical
connection of a flexible piezoelectric transducer to a structural
member adapted for use in an oil production system.
58. A method according to claim 57, further comprising receiving
electrical signals generated at the electrical connection of the
flexible piezoelectric transducer by acoustic energy in the
structural member.
59. A method according to claim 58, further comprising analyzing
the received electrical signals for indications of defects in the
structural member.
60. A method according to claim 58, further comprising applying an
external force to the structural member.
61. A method for detecting the flow of material through a tubular
element in a hydrocarbon production system, comprising bonding a
mechanical connection of a flexible piezoelectric transducer to a
tubular element adapted for flowing materials in an oil production
system.
62. A method according to claim 61, further comprising receiving
electrical signals generated at the electrical connection of the
flexible piezoelectric transducer by acoustic energy in the tubular
member.
63. A method according to claim 62, further comprising analyzing
the received electrical signals to identify materials flowing in
the tubular member.
64. A method according to claim 61, further comprising driving said
transducer with an electrical signal to induce vibrations in the
tubular element.
65. A method according to claim 64, further comprising analyzing
the response of the tubular element to the vibrations to measure at
least one parameter of fluid within the tubular element.
66. A method according to claim 65, wherein said parameter is one
of viscosity, density and ratio of water to oil.
67. A method for transmitting and receiving acoustic waves in a
tubular element in a hydrocarbon production system, comprising:
bonding at least first and second flexibly piezoelectric
transducers to a tubular element adapted for use in a hydrocarbon
production system, said transducers having a directional mechanical
connection, the mechanical connection of the first transducer
positioned at a first angle relative to the axis of the tubular
element, and the mechanical connection of the second transducer
positioned at a second angle relative to the axis of the tubular
element, the second angle being different from the first angle.
68. A method according to claim 67, wherein the first transducer is
substantially in alignment with the axis of the tubular element and
the second transducer is substantially out of alignment with the
axis of the tubular element.
69. A method according to claim 68 further comprising: receiving
acoustic waves with the first and second transducers, and analyzing
the received acoustic waves to estimate the distance to the source
of the acoustic waves.
70. A method according to claim 68, further comprising: using the
first transducer to telemeter data through the tubular element, and
using the second transducer to telemeter an acoustic wave which at
least partially cancels an acoustic wave generated by a noise
source.
71. Apparatus comprising: a section of a wellbore tubular member,
and a thin piezoelectric device bonded to the wellbore tubular
member.
72. Apparatus according to claim 71, wherein the thin piezoelectric
device has a length, a width and a thickness and has one of its
major planar surfaces bonded to a surface of the wellbore tubular
member.
73. Apparatus according to claim 72, wherein the thin piezoelectric
device has a mechanical response aligned with the length, and is
bonded to the wellbore tubular member with its length dimension in
alignment with the wellbore tubular member central axis.
74. Apparatus according to claim 72, further comprising: first and
second flexible insulating films, and interdigitated electrode
patterns carried on the first and second films, the first and
second films bonded to opposite major planar surfaces of the
device, with the electrode patterns in contact with the device and
in alignment with each other.
75. Apparatus according to claim 72, wherein the thickness
dimension is between 0.001 and 0.025 inch.
76. Apparatus according to claim 75, wherein the thickness
dimension is about 0.010 inch.
77. A system for monitoring health of a structural member,
comprising: a structural member adapted for use in an oil
production system, and a thin piezoelectric transducer bonded to
the structural member.
78. Apparatus according to claim 77, wherein the thin piezoelectric
device has a length, a width and a thickness and has one of its
major planar surfaces bonded to a surface of the structural
member.
79. Apparatus according to claim 78, further comprising: first and
second flexible insulating films, and interdigitated electrode
patterns carried on the first and second films, the first and
second films bonded to opposite major planar surfaces of the
device, with the electrode patterns in contact with the device and
in alignment with each other.
80. Apparatus according to claim 79, wherein the thickness
dimension is between 0.001 and 0.025 inch.
81. Apparatus according to claim 80, wherein the thickness
dimension is about 0.010 inch.
Description
CROSS-REFERENCE TO RELATED APPLICATIONS
[0001] Not applicable.
STATEMENT REGARDING FEDERALLY SPONSORED RESEARCH OR DEVELOPMENT
[0002] Not applicable.
REFERENCE TO A MICROFICHE APPENDIX
[0003] Not applicable.
FIELD OF THE INVENTION
[0004] This invention relates to piezoelectric devices used in
boreholes and oilfield structural members and more particularly to
the combination of encapsulated flexible piezoelectric devices with
tubular elements in a borehole and with structural members and use
thereof for sensing, actuation, and health monitoring.
BACKGROUND OF THE INVENTION
[0005] Piezoelectric devices are known to be useful as solid state
actuators or electromechanical transducers which can produce
mechanical motion or force in response to a driving electrical
signal. Stacks of piezoelectric disks have been used, for example,
to generate vibrations, i.e. acoustic waves, in pipes as a means of
telemetering information. Such transducers are used in drilling
operations to send information from downhole instruments to surface
receivers. The downhole instruments generally produce an electrical
waveform which drives the electromechanical transducer. The
piezoceramic stack is typically mechanically coupled to a pipe or
drill string by external shoulders. The transducer generates
acoustic waves in a drill pipe which travel through the drill pipe
and are received at another borehole location, for example at the
surface or an intermediate repeater location. A receiver may
include a transducer such as an accelerometer or another
piezoelectric device mechanically coupled to the pipe. The received
acoustic signals are converted back to electrical signals by the
receiving transducer and decoded to recover the information
produced by the downhole instruments.
[0006] Such piezoceramic materials have not typically been used for
other downhole purposes due to their size, shape and brittle
characteristics which make them incompatible with downhole
structures. Most downhole structures are tubular. There are few
flat surfaces for attaching piezoelectric materials. The shoulders
required for mechanically coupling the conventional piezoceramic
stacks extend from the outer surfaces of the tubular member, e.g.
drill pipe, and occupy precious space or require use of larger bits
or casing which increases drilling costs.
[0007] It would be desirable to provide other transducer structures
and applications useful in downhole assemblies and other oilfield
structures.
SUMMARY OF THE INVENTION
[0008] A system and method for converting electrical energy into
acoustic energy, and vice versa, in hydrocarbon production system
structural components. Thin and/or flexible piezoelectric
transducers have at least one major planar surface bonded to a
surface of a structural member. Flexible electrodes on the major
planar surfaces of the transducer are used to input electrical
energy to induce acoustic waves in the structural member or receive
electrical energy produced by acoustic waves in the structural
member.
[0009] In one telemetry embodiment, thin flexible transducers are
bonded to the surface of a borehole tubular element, such as a
drill string. Data collected by down hole instruments is encoded
into electrical signals which are input to the electrical
connection of he transducer. The transducer produces corresponding
acoustic waves in the borehole tubular element. Another transducer
of the same type may be bonded to the tubular element at another
borehole location to receive the acoustic waves and produce
corresponding electrical signals for a telemetry receiver.
[0010] In another embodiment, thin piezoelectric transducers may be
bonded to surfaces of structural members, or laminated into the
structure of composite structural members, for health monitoring.
Acoustic waves in the structure generated by mechanical defects are
received and used to identify the presence of the defects.
[0011] In another embodiment, thin flexible piezoelectric
transducers are bonded to flow lines for monitoring materials
flowing in the lines. Acoustic waves produced in the flow lines by
particulate matter can be received and used to identify the
particulate matter. Alternatively, the transducers can induce
vibrations in the tubular member and analyze the response to
determine characteristics of fluids flowing in the flow line.
BRIEF DESCRIPTION OF THE DRAWINGS
[0012] FIG. 1 is an illustration of a prior art borehole telemetry
transducer assembly using stacked piezoelectric transducers.
[0013] FIG. 2 is an illustration of a borehole telemetry transducer
according to one embodiment of the present invention.
[0014] FIG. 3 is an exploded view of a piezoelectric transducer
useful in the FIG. 2 embodiment.
[0015] FIG. 4 is a partial cross sectional view of the transducer
of FIGS. 2 and 3 illustrating an arrangement of electrodes and
resulting electric fields.
[0016] FIG. 5 is an illustration of placement of a plurality of
piezoelectric transducers on a signal transmission medium to
provide an encoded signal.
[0017] FIG. 6 is an illustration of placement of a plurality of
piezoelectric transducers on a signal transmission medium to
provide or sense compressional, torsional and hoop waves.
DETAILED DESCRIPTION OF THE INVENTION
[0018] For the purposes of this disclosure, an electromechanical
transducer or actuator is any device which can be driven by an
electrical input and provides a mechanical output in the form of a
force or motion. Many electromechanical transducers also respond to
a mechanical input, generally a force, by generating an electrical
output. For purposes of the present disclosure, each transducer is
considered to have an electrical connection and a mechanical
connection. Each connection may be considered to be an input or an
output or both, depending on whether the transducer is being used
at the time to convert electrical energy into force or motion or to
convert force or motion into electrical energy.
[0019] A piezoelectric device is an electromechanical transducer
which is driven by an electric field, normally by applying a
voltage across an electrical connection comprising a pair of
electrodes, and changes shape in response to the applied field. The
change of shape appears at the mechanical connection of the device.
Various crystalline materials, e.g. quartz, ceramic materials, PZT
(lead-zirconate-titanate), ferroelectric, relaxor ferroelectric,
electrostrictor, PMN, etc. provide piezoelectric responses. These
materials usually respond to mechanical force or motion applied to
their mechanical connection by generating an electric field which
produces a voltage on its electrical connection, e.g. electrodes.
As a result, a piezoelectric transducer can be used as an actuator
and as a sensor.
[0020] FIG. 1 is an illustration of a portion of a typical prior
art downhole telemetry system. A length of pipe 10 may be part of a
drill string in a borehole. In a drilling environment, the pipe 10
serves several purposes. It may transmit turning forces to a drill
bit on the bottom of the drill string and normally acts as a
conduit for flowing drilling fluid down the well to the bit. It may
also provide an acoustic signal transmission medium for sending
information from sensors or detectors in the borehole to equipment
at the surface location of the well.
[0021] Two rod shaped electromechanical transducers 12 are
mechanically coupled to the pipe 10 by upper and lower shoulders 14
and 16 which are attached to the pipe 10. The upper and lower ends
of the transducers 12 form their mechanical connections which are
coupled to the shoulders 14, 16. Mechanical forces generated by the
transducers 12 are coupled to the pipe 10 through the shoulders 14,
16. When the transducers 12 are driven with an oscillating
electrical signal, they induce a corresponding axial compression
signal in the pipe 10. It is desirable to have two transducers 12
spaced on opposite sides of pipe 10, as illustrated, and driven
with the same electrical signal to avoid applying bending forces to
the pipe 10.
[0022] The transducers 12 are typically made from a plurality of
circular or square cross section piezoceramic disks 18 stacked to
form the linear or rod shaped transducers as illustrated. Between
each pair of disks is an electrically conductive layer or electrode
20 which allows application of electrical fields to the disks.
Alternate electrodes are electrically coupled in parallel to form
the electrical connection of the transducers 12. Polarities of
alternate disks are reversed so that upon application of a voltage
between successive electrodes, each disk changes shape and the
entire stack changes shape by the sum of the change in each disk.
The transducers 12 can also be used to detect or receive acoustic
waves in the pipe 10 which will generate voltages between the
electrodes 20. This construction of a piezoelectric transducer is
conventional.
[0023] The stacked transducers 12 generally have a length between
shoulders 14 and 16 of about twelve inches and have a width of not
less than about one-tenth of the length. Thus, the width or
diameter of each transducer is generally not less than about 1.25
inch. With transducers positioned on opposite sides of the pipe 10
as illustrated, this transducer assembly adds about three inches to
the overall diameter of the pipe 10 assembly.
[0024] FIG. 2 is an embodiment of the present invention which can
provide the downhole telemetry transmission function of the prior
art system of FIG. 1 with a smaller overall diameter. A section of
a borehole tubular member 24 may be a portion of a drill pipe or
production tubing in a borehole. For purposes of the present
invention, a borehole tubular element need not have a cylindrical
shape, but may have flat surfaces and could have a square cross
section, e.g. a Kelly joint, so long as it has a closed cross
section through which fluids may be flowed. Mechanically bonded to
the outer surface of the member 10 are a plurality of thin flexible
piezoelectric transducers 26, 28 and 30. It is desirable for
transducer 26 to include at least two devices bonded on opposite
sides of pipe 24 at the same axial location. In the illustrated
embodiment, four transducers 26 are bonded to the pipe 24 at the
same axial location and radially displaced from each other by
ninety degrees. Each of the transducers 28 and 30 are likewise
illustrated as including four separate devices positioned like the
devices 26. The pipe 24 is shown as broken to indicate that more of
the transducers are bonded to the pipe 24 over a length of about
twenty-five feet which, for the particular devices 26, 28, 30
described below, will provide an acoustic energy level about the
same as a typical prior art device as illustrated in FIG. 1. The
devices 26, 28, 30 may be bonded to the surface of pipe 24 with an
adhesive, e.g. an epoxy adhesive. In this arrangement, the entire
surface which is bonded to the pipe surface forms the mechanical
connection of the transducer. For further strength they may be
wrapped with a protective layer of a composite layer, e.g.
fiberglass, a metal, e.g. steel, a polymer, e.g. glass impregnated
PTFE, etc. It may be desirable to surround the devices 26, 28 and
30 with a protective housing, such as a metal sleeve. Space between
the sleeve and the pipe 24 may be filled with a fluid such as oil
for pressure balancing. Such a protective housing would not only
provide protection from permanent damage to the devices 26, 28 and
30 but may isolate them from lesser contacts with other parts of
the well, e.g. the borehole wall, which may generate acoustic noise
and interfere with the intended functions of the devices.
[0025] In the embodiment of FIG. 2, at least one large planar
surface of the devices 26, 28 and 30 is bonded by an adhesive to a
surface of the pipe 24. For purposes of the present invention, the
term "bonded" means any mechanical attachment of the mechanical
connection of a transducer which causes the transducer to
experience essentially the same strains as the member to which it
is bonded. Thus in some cases, only the ends and or edges of the
devices 26, 28 and 30 may be attached by adhesive to a surface in
order for the strains to be the same. The devices 26, 28 and 30 may
be attached by adhesive to an intermediate part, e.g. a piece of
shim, which is attached to the surface by bolting, welding, an
adhesive, etc. In similar fashion, a wrap of a protective composite
may bond the devices to the surface sufficiently to ensure that the
strains are shared. Thus, the prior art devices 12 of FIG. 1 may be
considered bonded to the pipe 10 by being clamped between shoulders
14 and 16, whether or not an adhesive is used to attach the
mechanical connections, i.e. the ends, of the devices 12 to the
shoulders 14 and 16.
[0026] FIG. 3 illustrates one embodiment of the structure of a
transducer 34 which may be used for each of the devices 26, 28 and
30 of FIG. 2. The center of device 34 may be formed of a thin
rectangular slab 36 of piezoceramic which has been machined to be
made flexible. A series of grooves 38 have been machined, e.g. by
laser etching, along the long dimension of the slab 36. The grooves
make the slab flexible, especially across its short dimension. The
grooved piezoceramic slab 36 may be made according to the teachings
of U.S. Pat. No. 6,337,465 issued to Masters et al. on Jan. 8, 2002
which is incorporated herein for all purposes.
[0027] Two flexible insulating sheets 40 and 42 are bonded to the
upper grooved and lower ungrooved surfaces of the slab 3, by for
example an epoxy adhesive. In this embodiment, the flexible sheets
40 and 42 are made of a copper coated polyimide film, e.g. a film
sold under the trademark Kapton. The copper coating has been etched
to form a set of interdigitated electrodes 44 and 46 on sheets 40
and 42. The electrodes 44, 46 are shown in phantom on sheet 40
because in the exploded view, they lie on the lower side of sheet
40. The electrodes 44 and 46 form the electrical connection for the
completed transducer 34. When the sheets 40 and 42 are attached to
the slab 38, the electrodes 44 and 46 are positioned between the
sheets 40, 42 and the slab 36.
[0028] FIG. 4 provides a cross sectional view of a portion of the
device 34 of FIG. 3. In FIG. 4, the center piezoceramic material 36
is shown sandwiched between the insulating sheets 40 and 42, with
the electrodes 44 and 46 in contact with the slab 36. The
electrodes 44 and 46 on the sheets 40 and 42 are aligned so that
electrodes 44 lie opposite each other and electrodes 46 lie
opposite each other as shown. A typical electrical field pattern is
illustrated for the case where electrodes 44 are positive and the
electrodes 46 are negative as indicated by the plus and minus
signs. The arrows 48 indicate the fields generated within the
piezoceramic material 36 by this condition. The key point is that
the field is basically in alignment with the long dimension of the
rectangular piezoceramic slab 36. This is desirable for providing
improved mechanical output in response to applied electrical
potential. This preferred mechanical response is a change in the
long dimension of the slab 36, that is it is a directional
response. When the device 34 mechanical connection is bonded to the
surface of a structural member, the dimensional change is
transferred or applied to the structural member. In an alternative
arrangement, each sheet 40 and 42 may be covered by a complete
copper film forming two electrodes which could be oppositely
charged. The resulting field would be from top to bottom of the
slab 36, which would provide a smaller mechanical response than is
provided by the illustrated arrangement. One benefit of this
alternative arrangement is a lower driving voltage requirement.
[0029] Currently available devices 34 have a length of about 2.5
inches and a width of about one inch. The thickness of slab 36 may
be from about 0.001 inch to 0.500 inch. For use in embodiments
described herein, the thickness may be from about 0.005 to about
0.025 inch. The length is desirably at least twenty times the
thickness to minimize end effects. Greater thickness provides more
mechanical power, but reduces the flexibility of the devices.
Devices as shown in FIG. 3 having a slab 36 thickness of about
0.020 inch can be bent around and bonded to a pipe having an outer
diameter of about 3.5 inches or larger. For a thickness of about
0.010 inch, the devices can be bent around a pipe having an outer
diameter of about one inch or larger. For best acoustic impedance
match, it would be desirable for the thickness of slab 36 to equal
the wall thickness of the pipe to which it is bonded. Generally,
this is not practical because this would result in a transducer
which would be too stiff to be bent around the pipe, and, as
explained below, too thick for generation of desired electrical
fields at practical voltages. Thus, the specific dimensions of the
flexible transducers used in the FIG. 2 embodiment will be selected
according to the available material lengths and widths. Thinner
slabs 36 or multiple devices 34 may be stacked to create the
transducer behavior of a thicker slab without compromising the
flexibility of the device and without requiring undesirable driving
voltages.
[0030] The thickness of the slab 36 also affects the electrical
connection of the device 34. As the device is made thicker, the
electrode voltage needed to provide a desirable field increases.
Use of thinner devices allows use of lower driving voltages which
is desirable. When these electrical interface considerations are
considered along with the flexibility factors, a slab thickness of
about 0.010 inch provides a good compromise. As noted above,
multiple devices may be stacked to increase mechanical power, while
maintaining mechanical flexibility and low driving voltage.
[0031] Other flexible piezoelectric transducers may be used in
place of the particular embodiment shown in FIG. 3. For example,
U.S. Pat. Nos. 5,869,189 and 6,048,622 issued to Hagood, IV et al.
on Feb. 9, 1999 and Apr. 11, 2000, which are incorporated herein
for all purposes, disclose a suitable alternative. The Hagood
transducer uses a plurality of flexible piezoceramic fibers aligned
in a flat ribbon of a relatively soft polymer. Flexible electrodes
like those shown in FIG. 3 and FIG. 4 are positioned on opposite
sides of the composite transducer for activating the device.
Flexible piezopolymers may also be used in relatively low
temperature applications. This temperature limitation normally
prevents using piezopolymers in downhole applications. Current
piezopolymers also lack sufficient stiffness or induced stress
capability to be used for structural actuation.
[0032] In addition to the continuous fibers disclosed in the Hagood
patent, a piezoelectric composite can be created in other forms.
The fibers can be woven fibers or chopped fibers. Additionally, the
composite can be formed with particulate piezoelectric material.
The particulate piezoelectric material may either be floating or it
can be arranged into chains, for example with electrophoresis.
[0033] The flexible transducers of the present invention share
important advantages over the prior art structure shown in FIG. 1.
They are manufactured as a flat device, which is much more
practical than attempting to manufacture a rigid curved
piezoceramic transducer to fit a particular tubular element, i.e.
an element with a given diameter. Since they are flexible, they
will conform to any curved surface within the limits of their
flexibility, i.e. they fit a range of tubular goods with a range of
diameters. They may be bonded directly to the surface of metal
tubular goods or may be laminated into the structure of composite
tubular goods useful in down hole systems or other oilfield
structural components. The flexibility of the devices is in part
achieved by using thin slabs or fibers of piezoceramic material.
The devices are extremely thin when compared to the prior art
devices. As a result, the flexible devices do not effectively
reduce clearances or require larger casing, etc. Normally they may
extend from the tubular element by less than conventional joints or
collars for which clearances are already provided. The fact that
the flexible piezoelectric devices are made primarily of a parallel
set of linear fibers or rods makes them inherently directional in
their acoustic outputs. As a result of these advantages, there are
numerous applications for flexible piezoelectric devices in down
hole and other oilfield environments.
[0034] The piezoelectric devices used in the embodiments described
herein are distinguished from the prior art devices in both being
thin and flexible. They are also distinguished by the fact that the
electrodes, e.g. 44 and 46 of FIG. 3, forming the electrical
connection lie on surfaces which are parallel to the long dimension
of the devices, which is also the direction of primary mechanical
output of the devices. This direction is also parallel to the
surface of the borehole structure, e.g. drill pipe, to which the
piezoelectric device is bonded. In contrast, the prior art stacked
devices of FIG. 1, use electrodes which lie in planes perpendicular
to the primary mechanical output direction and extend all the way
through or across the stack. As discussed above, to have sufficient
flexibility to be bonded to or in tubular goods, the devices are
preferably thin as indicated by dimensions listed above. The
devices are as a minimum sufficiently flexible to bend, without
substantially degrading performance, with the structural members to
which they are bonded, even if they are bonded to a flat surface.
The structures to which the devices are bonded in the described
embodiments all experience large forces and will bend to some
extent. To be considered thin for purposes of the present
invention, the devices of the present invention must also be thin
enough to allow application of sufficient field strength, e.g. the
fields 48 of FIG. 4, at voltages which are reasonably achievable in
an oilfield down hole environment. In the prior art stacked
devices, the thickness of the individual disks may be adjusted for
the available voltage, since the electrodes extend all the way
through or across the stacked device. The devices of the present
invention must be thin enough for sufficient fields to be generated
by the electrodes on the main planar surfaces of the devices as
illustrated in the drawings.
[0035] One use of the system shown in FIG. 2 is a downhole data
telemetry system. This is the same application as described for the
prior art device of FIG. 1. Each of the plurality of transducers
26, 28, 30 may be electrically connected together and driven by the
output of an electronic transmitter and/or receiver package 29 on a
drill string, e.g. part of a logging while drilling system. Data
collected by the package, e.g. temperature and pressure, may be
digitally encoded and then transmitted up the drill string as
acoustic waves. For example, in a dual tone system, a digital one
may be transmitted as a first frequency acoustic signal and a zero
as a second frequency acoustic signal. The telemetry driver
supplies the desired frequency electrical signals to the
transducers 26, 28 and 30, and they generate acoustic waves in the
drill pipe 24 at the same frequencies. The signals travel up the
drill pipe and may be detected by a similar set of transducers
attached to a length of drill pipe at the surface of the earth or
at an intermediate repeater location. The original digital data may
be recovered from the detected signals.
[0036] As noted above, it may take a plurality of flexible
transducers 26, 28, 30 bonded to about twenty-five feet of pipe 24
to generate acoustic power equivalent to the power produced by the
prior art stacks shown in FIG. 1. The system of this embodiment
allows an alternative driving system to be used, which effectively
provides the same power level with only about a ten-foot series of
the transducers 26, 28 and 30. Instead of wiring all of the
electrical connections of transducers 26, 28 and 30 together so
that they are driven in phase, they may be driven separately as a
phased array. For example, the acoustic velocity in the pipe 24 can
be measured. The distance between transducers 26 and 28 is known.
At a given signal frequency, it is therefore possible to determine
the phase shift or time delay between acoustic signals generated at
transducers 26 and 28. The electrical input signal to transducer 28
can be delayed relative to the signal applied to device 26 by the
appropriate phase shift or time delay so that the acoustic signal
generated by transducer 28 is in phase with the acoustic signal
from transducer 26 when reaches the location of transducer 28.
Likewise the electrical signal driving device 30 can be delayed by
an amount appropriate to provide acoustic waveform reinforcement to
the wave traveling up the pipe 24 from transducers 26 and 28. For
equally spaced transducers 26, 28, 30 the shift or delay between
each pair would be the same. Note that the reinforcement is
directional. That is, the signal may be reinforced in the desirable
upwardly traveling direction while it is reduced in the downward
traveling direction. The signal reinforcement allows generation of
a larger acoustic signal in the desired direction with less of the
transducers.
[0037] Further telemetry enhancement may be achieved by using the
same phased array approach for a receiving array of transducers. A
set of transducers identical to the transducers 26, 28, 30 of FIG.
2, may be bonded to the drill string up hole from the transmitter
The electrical connections from each set may be connected through
corresponding time delays or phase shifts before they are combined
in a receiver. This phasing again makes the array directional and
effectively improves gain of the receiver.
[0038] The phased array arrangement may also be used to advantage
in a repeater which receives signals from a lower down hole
location and retransmits it to an up hole location such as another
repeater or the final receiver at the well head. Two arrays of
transducers as shown in FIG. 2 may be part of a repeater. One can
be used with a receiver phased to receive acoustic waves
preferentially from down hole. Another can be used with a
transmitter phased to transmit signals preferentially up hole.
Alternatively, a single array may be used for both the receiver and
the transmitter. That is, the receiver with inputs phased for
receiving from down hole can be coupled to the same set of
transducers as a transmitter with outputs phased to cause the
transducer array to transmit up hole.
[0039] FIG. 5 illustrates another embodiment which provides an
improved signal transmission capability. A drill pipe 50 is shown
with a series of transducer pairs 52, 53, 54, 55, 56 and 57. The
spacing between pairs progressively increases from the closest
spacing between devices 52 and 53 to the greatest spacing between
devices 56 and 57. If these devices 52-57 are driven with an
impulse or short tone signal, a coded series of acoustic waves will
be generated in the pipe 50. This type of signal is similar to a
chirp signal. If a set of transducers having the same spacings is
attached to another portion of the pipe 50 as a receiver with its
electrical connections wired in series, the detected signals will
reinforce and generate an enhanced output when the specific
waveform produced by the transducers 52-57 is detected. The
spacings between adjacent transducers 52-57 need not be in the
simple progression shown in FIG. 5, but may be in a random order of
different spacings. Two sets of transducers with different spacing
sets may be used to represent a digital one and a digital zero for
telemetry purposes. Some of the transducers may be shared between
the two sets. The uniformly spaced transducers 26, 28, 30 of FIG. 2
may be used to produce such coded signals if each transducer is
individually driven so that random sets of the transducers can be
selected for transmission. In any case, the use of flexible
piezoelectric transducers according to these embodiments provides
telemetry encoding and signal directional enhancement which was
much less practical with prior art systems.
[0040] In the FIG. 2 embodiment, the long dimension of transducers
26, 28, 30 is aligned with the axis of the tubular member 24. Since
the transducers are directional, this is an efficient way to
produce axial compression waves in the pipe 24. It may be desired
to transmit information with other types of mechanical waves, e.g.
torsional mode, hoop mode, etc.
[0041] FIG. 6 illustrates a multimode set of transducers bonded to
a tubular element 60 to produce three different wave modes. Four
devices 62 are bonded to the element 60 with long dimensions
aligned with the central axis of element 60. These are positioned
like the transducers 26, 28 and 30 of FIG. 2, and will primarily
produce or detect axial compression waves in the element 60 if they
are driven with the same signal. If desired, the devices 62 may be
driven separately and out of phase to generate flexural waves in
the pipe 60. Four other devices 64, which may be identical to
devices 62, are bonded to the element 60 at an angle of about
thirty to sixty degrees relative to the central axis of pipe 60. In
the FIG. 6 embodiment, they are shown positioned at about
forty-five degrees. Since the devices are directional and generate
forces in alignment with the long dimension of the devices 64,
these devices will produce, or detect, torsional waves in the
element 60. Another set of transducers 66 is shown bonded to the
element 60 with their axes positioned perpendicular to the central
axis of the element 60. When devices 60 are driven, they will
change the radius of the pipe and create hoop waves. Likewise,
devices 60 will preferentially detect hoop waves. While the
structure of the transducers 26, 28, 30 makes them more flexible
across their width than their length, they are also flexible along
their long dimension and can be bonded to a tubular element at an
angle as illustrated for devices 64 and 66.
[0042] The transducer array of FIG. 6 allows transmission or
detection of essentially all acoustic wave modes which may be
intentionally carried on an element in a borehole. It also allows
detection of essentially any form of acoustic noise which may be
generated by drilling or production operations in a well. An array
of the sets of transducers as shown in FIG. 6 may be positioned
along a length of a tubular element in the manner illustrated in
FIG. 2 or in FIG. 5. This arrangement allows selective transmission
of telemetry by any mode, e.g. compression, torsional, hoop or
flexural mode. The particular mode may be chosen based on noise
levels occurring in a well at the time. An array allows use of
directional or coded signals as discussed above in any wave
mode.
[0043] The multimode transducer set of FIG. 6 also allows detection
and cancellation of various noises which may interfere with
acoustic telemetry. Acoustic noise may be generated in borehole
elements by numerous sources. The drill bit is a large source of
acoustic noise. But noise may also be generated by contact of a
drill string with a borehole wall at any point along its length.
Noise from any source may travel up the drill string by more than
one mode, e.g. both compression and torsion waves. However, the
different wave modes travel at different velocities. By detecting
all wave modes with a set of devices 62, 64, 66, and processing the
signals to determine arrival time differences, the distance to the
noise source can be determined. This could indicate excessive wear
occurring on a drill pipe and identify the depth at which it is
occurring.
[0044] It is common for a drill bit to generate large torsional
noises in a drill string which may interfere with acoustic
telemetry even in other modes. The multimode transducer set of FIG.
6 may allow cancellation of torsional noises while simultaneously
transmitting telemetry using compression waves. Thus torsional
noise from a drill bit may be detected by one or more torsional
devices 64. A noise cancellation processor may then transmit a
torsional wave out of phase with the noise to at least partially
cancel the upward traveling torsional noise. This would provide a
better condition for compression wave telemetry using the axially
aligned devices 62.
[0045] The same piezoelectric transducer can be used as an actuator
to create the telemetry waves as well as a sensor to sense the
telemetry waves. By measuring both the voltage and the charge, a
single piezoelectric device can be used simultaneously as a
actuator and a sensor.
[0046] The individual transducers, e.g. 26, 28, 30 of FIG. 2, need
not have the simple rectangular shape as shown in the figures. It
may be desirable to taper the shape of the transducers. For example
they may be more narrow at their ends than in the center, e.g. a
football, circular, or diamond shape. Such shaping may allow
generation of specially shaped acoustic waves or better impedance
matching of the transducers 26, 28, 30 to the tubular members to
which they are bonded. The shape of the electromechanical coupling
of the transducer can be tapered by changing the spacing of the
electrodes, by changing the density of piezoelectric fibers, or by
changing the pattern etched by the laser.
[0047] The embodiments described herein may also be used for
structural health monitoring. With reference to FIG. 2, transducers
26 and 30 may be used to determine if any structural defects, e.g.
cracks, have occurred between the two transducers. When the system
is installed, signals may be transmitted from transducer 26 and
received by transducer 30. A record of signal strength, phase
shift, spectral content etc. can be made. From time to time, the
test transmission can be repeated and compared to the original
records. Changes in the signal transmission can indicate cracks or
other defects in the structure between the transducers 26 and 30.
This arrangement can be used on any tubular or other structural
members in a borehole, on subsea risers, flow lines, platform
support members, etc. Sets of the multimode transducers of FIG. 6
may allow more detailed collection of health monitoring information
for a tubular element.
[0048] Many of these structural members, flow lines, etc. are being
made of composite structures instead of metal. The composite
structures may include fibers of glass, carbon, graphite, ceramic,
etc. in a matrix of epoxy or other resin or polymer. As noted
above, the transducers may be imbedded in the composites at the
time of manufacture. Devices imbedded in composites may be used
without conductors, i.e. wires, extending from imbedded transducers
to the outer surface of the structural member. The flexible
insulating films 40, 42 of FIG. 2 can be extended to include
antenna structures and integrated surface-mount electronics and
batteries for coupling signals to and from the transducers.
Transponders can be placed close to the transducers for coupling
signals through the composite materials to and from the
transducers. This arrangement may be particularly useful for health
monitoring tests which may be performed on a monthly or yearly
schedule.
[0049] Structural health monitoring may also be done with a single
piezoelectric transducer, especially one laminated into a composite
structure. The capacitance of the device can be measured by the
driving circuitry. Any delamination of the composite structure at
the transducer will change the measured capacitance of the device.
A device used for telemetry purposes can also be used for health
monitoring. A single transducer can be used to "listen" for signs
of structural failure. As cracks form, they make distinctive sounds
which are often relatively easily detected by a transducer imbedded
in the structure. A structure with cracks or delaminations may also
make distinctive noises as it flexes during normal operations. For
example, a composite subsea riser moves in response to wave action
and currents and these movements create noises at structural
defects. Forces may intentionally be applied to such structures to
cause motion and stress which would create detectable noises at
structural defects. Intentionally applied forces may provide a more
quantitative measure of structural health, since the applied force
may be known or measured. The transducers of the present invention
are particularly suited to these applications because of relatively
large profile in length and width and the distributed arrangement
along structural members. These transducers are more likely to
detect such defects than a point source type of transducer.
[0050] The disclosed embodiments are also useful for vibration
sensing. They are sensitive enough to detect some vibrations caused
by solids, e.g. sand, in produced fluids. Vibrations caused by the
flowing fluids themselves may also be detected. Since many fluids
flow in relatively small diameter flow lines, the flexible
piezoelectric transducers are particularly suited to these
applications. They may be bonded directly to the inner or outer
surfaces of the flow lines, or may be laminated into the wall of a
composite flow line, to detect such vibrations. Flow lines are one
of the popular applications of composite materials in which the
flexible transducers may be imbedded. Since the piezoelectric
devices are self-powered, electrical connections may be made
directly from the transducer electrodes to the input of a suitable
amplifier and recording system, etc. to detect the vibrations. The
systems may include spectral analyzers for identifying frequencies
and/or patterns or signatures which are known to be produced by
particular failure mechanisms.
[0051] The disclosed embodiments may be used for detecting the flow
of fluids other than solids as discussed above. It is desirable in
producing oil and gas wells to determine the composition of fluids
flowing in a flow line. The fluids typically are a mixture of oil
and/or gas and/or water. If turbulent flow is created at the
location of a transducer as described above, the noise generated by
the flow can be analyzed to identify the types of fluids in the
flow line. Turbulence can be created by providing a constriction or
upset in the flow line. Thus could assist with particle or fluid
flow detection.
[0052] The hoop mode transducers 66 of FIG. 6 may also be used for
evaluation of fluids in a flow line. A hoop mode wave at one or
more frequencies may be generated in a flow line by devices 66. The
response of the flow line will depend on the density, viscosity and
other characteristics of fluid in the line. The resonant frequency
may be measured and used to estimate fluid parameters.
[0053] In addition to simply receiving signals for telemetry,
health monitoring, etc. the piezoelectric devices used in the
various embodiments may also be used for power generation. As noted
above, the structural members used in hydrocarbon producing
facilities typically experience large forces, strains, etc. This
represents a large amount of available energy. By attaching
appropriate rectifying and conditioning circuitry to the electrical
connections of downhole piezoelectric devices, electrical power may
be generated. This is especially useful for recharging down hole
batteries used to power various sensors and telemetry
equipment.
[0054] In many of the above-described applications of the flexible
piezoelectric transducers, it may be desirable to provide reactance
balancing by combining an inductive type of transducer with a
piezoelectric device as described herein. This approach is
described in more detail in a co-pending U.S. patent application
Ser. No. ______, attorney docket 1391-39200, entitled Hybrid
Piezoelectric and Magnetostrictive Actuator, by inventors Michael
L. Fripp and Roger L. Schultz, filed on the same date as this
application and assigned to the same assignee, which application is
hereby incorporated by reference for all purposes.
[0055] It is apparent that various changes can be made in the
apparatus and methods disclosed herein, without departing from the
scope of the invention as defined by the appended claims.
* * * * *